Amplification of the Epidermal Growth Factor Receptor gene (EGFR) represents the most common oncogene activation event in glioblastoma, the most common and malignant form of brain tumor. In the vast majority of glioblastomas, EGFR amplification is accompanied by EGFR mutation. Little is known, however, about the functional and biologic consequences of the mutations that have been identified. Understanding these consequences is important because many of the therapies that are under consideration for the treatment of cancer patients rely upon the effects of inhibitors intended to block the function of receptor tyrosine kinases such as EGFR, or the signaling proteins downstream of these receptors. Here we propose to initiate a systematic analysis of mutant EGF receptors known to be expressed in human glioblastomas. This analysis will be accompanied by studies examining the effects of chemical inhibitors, as well as dominant-negative proteins, on wild type and mutant EGF receptor signaling, and will include a collaborative investigation with Dr. Allan Yates (Project 4) to examine the effects of an endogenous glycolipid, GM3, on EGF receptor function. The project also contains a clinical translational component that will determine whether EGFR amplification, amplification level, and/or specific types of EGFR mutations confer a particularly poor prognosis for subsets of malignant glioma patients. In total it is anticipated that the information obtained through the implementation of this project will lead to an improved understanding of EGF receptor structure-function relationships, and an ability to exploit this understanding for the treatment of patients afflicted with this cancer.